Many structures are built using concrete, including, for instance, buildings, parking structures, apartments, condominiums, hotels, mixed-use structures, casinos, hospitals, medical buildings, government buildings, research/academic institutions, industrial buildings, malls, roads, bridges, pavement, tanks, reservoirs, silos, sports courts, and other structures.
Prestressed concrete is structural concrete in which internal stresses are introduced to reduce potential tensile stresses in the concrete resulting from applied loads; prestressing may be accomplished by post-tensioned prestressing or pre-tensioned prestressing. In post-tensioned prestressing, a tension member is tensioned after the concrete has attained a desired strength by use of a post-tensioning tendon. The post-tensioning tendon may include for example and without limitation, anchor assemblies, the tension member, and sheaths.
Traditionally, a tension member is constructed of a material that can be elongated and may be a single or a multi-strand cable. The tension member may be formed from a metal, such as reinforced steel. The tension member is encapsulated within a polymeric sheath hot extruded thereabout to form an encapsulated tension member. The sheath may prevent or retard corrosion of the tension member by restricting exposure of the tension member to corrosive or reactive fluids. Further, the sheath may prevent or retard concrete from bonding to the tension member. The sheath may be filled with grease. Because the tension member and the polymeric sheath are formed from different materials, the thermal expansion and contraction rates of the tension member and polymeric sheath may differ. When the encapsulated tension members are coiled for transport and storage, uneven thermal contraction may occur as the tendon cools. When installed as part of the post-tensioning tendon in a pre-stressed concrete member, cooling of the sheath may cause separation of the sheath from an anchorage, potentially exposing the tension member to corrosive or reactive fluids.
The post-tensioning tendon traditionally includes an anchor assembly at each end. The tension member is fixedly coupled to a fixed anchor assembly positioned at one end of the post-tensioning tendon, the “fixed-end”, and stressed at the stressed anchor assembly positioned at the opposite end of the post-tensioning tendon, the “stressing-end” of the post-tensioning tendon.
When coupling the tension member to the stressed anchor assembly positioned at the stressing-end of the post-tensioning tendon, the sheath at the stressing-end is retained within the stressed anchor assembly, such as, for instance, by coupling the sheath within a sheathing retainer. Examples of sheathing retainers include a sheathing lock and a sheathing retention capsule. The sheathing retainer holds the sheathing in the stressed anchor assembly, such as through the use of wedges. During installation, the sheath may be decoupled from or improperly coupled to the sheathing retainer. For example, decoupling or improperly coupling to the sheathing retainer may be caused by: (1) cutting a portion of the sheathing to expose a portion of the strand, where the sheath is cut too short to couple with the sheathing retainer; (2) applying tension applied to the sheath, resulting in shrinkage of the length of the sheath over time; or (3) applying force applied to the sheath causing stretching of the sheath, or shortening of the sheath. During installation, tension may be applied to the sheath from stepping on the sheath or impact by tools or heavy equipment. Traditionally, solutions for a sheath that is too short or is otherwise decoupled from the sheathing retainer include applying tape about the unsheathed portion of the tension member, or splicing additional sheath onto the existing sheath.